Digital tape drawing system

ABSTRACT

A system that provides a bimanual user interface in which an input device is provided for each of the users hands, a left hand (LH) device and a right hand (RH) device. The input devices are used in conjunction with a large format, upright, human scale display at which the user can stand and upon which the input devices are moved. The positions of the input devices on the display are marked by displayed cursors. The system detects the position of the input devices relative to the display and draws a vector corresponding to unfastened tape between positions of cursors of the corresponding input devices and pointing from the LH device to the RH device. By changing the state of the LH input device the unfastened tape can be fastened or pinned along the vector as the user moves the LH device toward the RH device. By changing the state of the RH device, the tape can be unfastened by moving the LH device away from the RH device. Straight lines are drawn by holding the RH fixed while the LH pins the tape. Curves are drawn by moving the RH device while the LH device pins the tape. The switch between straight and curved lines occurs without an explicit mode switch simply by keeping the RH device fixed or moving it. The radius of the curvature of curved lines corresponds to the separation between the LH and RH devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a computer tool designed to enhanceand replace the physical tape drawing process used in design studiosand, more particularly, is directed to tool operation on a large scaledisplay screen, with two handheld input sensors which allows for asmooth modeless transition between creating straight lines and curves.

2. Description of the Related Art

Designers in the automobile industry have traditionally created conceptsketches of cars on large scale upright surfaces (walls) that preserve a1-1 or “full-size” scale factor between the sketch and the finalphysical car. The main reason for these full-size upright sketches isthat designers and managers want to determine and evaluate the principlecurves of a design as early as possible in the design process. Workingat 1-1 scale is critical to this, if one wants to avoid the unpleasant“surprises” that might otherwise occur if work were done at a reducedscale or on a conventional CRT, for example. While these measures mayseem extreme, it is important to recognize that the product beingdesigned could cost up to $1 billion to bring to market. As such,minimizing mistakes is of utmost importance.

An interesting aspect of these concept sketches is that they are creatednot by using pencils and paint, but mainly by laying down black drafterstape that feels like common masking tape on the drawing surface.

This style of sketching with drafters tape, called “tape drawing”, isachieved by using the everyday skills of unrolling the tape with onehand and sliding the other hand along the tape while fastening it on thesurface. Even though the mechanics of this naturally two-handedtechnique are easily explained, the artwork created by experiencedpractitioners reflects a level of skill that is on a par with any otherartistic medium.

Tape drawing has several fundamental advantages over free-form sketchingwith a pencil, given the large scale size of the sketches. Firstly, itis difficult to draw, freehand, straight lines and smooth continuouscurves at this scale. Physical aids such as rulers and french curveswould assist the process, however, they would have to be of similarlarge scale which unfortunately makes them unwieldy for upright use.Drawing with tape, on the other hand, easily facilitates the generationof perfectly straight lines and, due to the slight elasticity of thetape which allows it to be deformed, smooth continuous curves as well.The freehand nature of the interaction is maintained, and yet the tape'scapabilities help regulate the user's actions to allow for creation ofsmooth continuous lines. In addition, tape drawing has the benefit ofeasily undoing actions and editing compared to drawing with pencils ormarkers. An undo is achieved simply by lifting the tape off the surface.Editing is performed in two ways: first, by lifting the tape off thesurface and relaying it, and second, by tearing off strips of tape andreplacing the strips with new tape as required.

While the advantages inherent in drawing with tape have ensured itsplace in the automotive design process, there are nonetheless severalproblems with this medium.

Firstly, of all the artists working on the initial design, the skill ofthe tape artist is the farthest removed from traditional computergraphics systems, and yet, the results of their work must eventually betransferred into the computer. While the resolution and fidelity of thetape from both the input and output perspectives are extremely high,there is no easy way to retain this fidelity when transferring theinformation to electronic formats. Currently, this transfer process isdone laboriously by digitizing the key curves of the tape drawing usinga hand-held position sensor and then recreating these curves in a CADpackage. This transfer process invariably introduces inaccuracies in theelectronic version which then have to be identified and removed. Also,since designers create multiple 2D tape drawings which representdifferent views (such as a front view and side view) of the under-lying3D vehicle, these 2D drawings have to be integrated when creating thefinal 3D model of the vehicle. This integration requires carefulalignment and matching of the primary curves of the model, a processthat can also introduce errors.

The second major problem with tape drawings is the difficulty in storingand retrieving old drawings. These drawings are typically done onstretched Mylar surfaces which when untacked or removed from the wallcontract and distort the drawing. Yet, this must frequently be done toaccommodate changes in the engineering drawings that typically underlaythe Mylar surface on which the tape drawing is done. Once the drawing istaken down, the purity and accuracy of the original drawing cannot bemaintained. Also, the tape itself tends to fall off the Mylar surfaceafter a period of time.

Finally, the physical nature of these drawings preclude easy sharing ofdesign information between different design studios.

What is needed is a digital tape drawing system that will alleviatethese disadvantages of physical tape drawing and which would reduce theerrors when transferring, retrieving and storing the tape drawings. Anelectronic system could also provide functionality beyond what ispossible using the traditional media.

However, given the aversion of most tape artists to current computermodeling software that require them to learn new skills unrelated totheir art, what is needed is a system that will retain the simplicity,fluidity, and capabilities of the physical tape drawing techniques.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a digital tapedrawing system that has the capabilities of drawing with physical tapeon a large surface.

It is another object of the present invention to provide a system thatallows drawing with a bimanual user interface which allows a user to useboth hands to draw.

It is a further object of the present invention to provide a system thatallows mode switching without an explicit mode switching operation.

It is also an object of the present invention to provide mode switchingresponsive to proximity or closeness of the input devices to each otherin the interface.

It is an object of the present invention to provide a user interface anddisplay system of a large scale suitable for drawing large objects, suchas automobiles, at a 1 to 1 scale.

It is also an object of the present invention to provide mode switchingthat is dependent on which combination of hand(s) are moving at a giventime.

It is another object of the present invention to provide a system thatallows for drawing of both curves and straight lines without an explicitmode switch.

It is also an object of the present invention to provide a system thatallows the smoothness and continuity of curves to be controlled directlyand simply by using the input gestures of the user's two hands.

The above objects can be attained by a system that provides a bimanualuser interface in which an input device is provided for each of theusers hands. The input devices are used in conjunction with a largeformat upright display at which the user can stand. The system detectsthe position of the input devices relative to the display and drawsunfastened tape between positions of cursors corresponding to the inputdevices. By changing the state of the input devices the unfastened tapecan be fastened or pinned and unfastened as the user moves one or bothinput devices relative to each other. During pinning, as the pinninghand moves toward the non-pinning hand, corresponding portions of theunfastened tape are pined. During unfastening a similar correspondencebetween the reverse movement of the input devices and the unfastenedtape occurs. Straight lines are drawn by holding the non-pinning handfixed while the pinning hand pins the tape. Curves are drawn by movingthe non-pinning hand while the pinning hand pins the tape. The switchbetween straight and curved lines occurs without an explicit mode switchsimply by keeping the non-pinning hand fixed or moving it. The radius ofthe curvature of curved lines corresponds to the separation between thehands as well as the magnitude of simultaneous movement of the twohands. A single input device can also be used to cut the tape and removeit from the display.

These together with other objects and advantages which will besubsequently apparent, reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the hardware components of the invention.

FIG. 2 is a state diagram of the states of the operations performed bythe present invention.

FIGS. 3A and 3B show unfastened tape drawing.

FIG. 4 illustrates the operations performed in drawing unfastened tape.

FIGS. 5A-5D show tape sticking, unsticking and terminating.

FIG. 6 illustrates the operations in tape sticking or fastening.

FIG. 7 illustrates the operations of tape unsticking or unfastening.

FIG. 8 illustrates the operations in tape termination after sticking.

FIGS. 9A-9E show curve and straight line drawing without explicit modeswitching.

FIGS. 10A-10D show tape cutting.

FIG. 11 illustrates the operations in tape cutting.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention alleviates the disadvantages of a traditional tapedrawing technique, while retaining its advantages. The inventionpreferably includes a large scale display screen and a virtual tapedisplayed on the screen. Two input devices are preferably used tocontrol the tape: the left hand device controls the “pinning” point ofthe tape, while the right hand device “dispenses” the tape. Thus, avirtual tape is formed between the two hands. The virtual tapepreferably is presented as a straight line, however, it conceivablycould be a higher order curve. A button on the left hand (LH) device (orpinning device) allows for lines/curves to be drawn on screen while thebutton is pressed. A button on the right hand (RH) device allows forediting (or cutting) of tape segments. Several important featuresresulting from the invention are described below.

The invention provides a technique for creating straight lines andcurves that allows a smooth, modeless transition between these two typesof lines. Current computer drawing techniques allow for either curvedrawing OR line drawing as separate tools/modes. The invention allowsboth to be done within one tool. This is achieved by using two inputsensors, one operated by each hand. Mimicking the manipulations ofphysical tape, the right hand sensor stretches the “virtual tape”, whilethe left hand sensor is used to pin down portions of the virtual tape.This pin position is constrained to lie along the virtual tape from theLH to the RH sensor. To draw a straight line, the right hand sensor iskept stationary, while the left hand sensor runs along the virtual tapetowards the RH, pinning it. The pinning action extends the current line.To draw a curve, both hands are moved simultaneously.

The invention allows a smoother curve to be produced than can beobtained by simple free-hand sketching. The existence of a virtual tapevector (from left hand sensor to right hand sensor) ensures that eachpinned data point lies on this vector. Thus, the direction of thevirtual tape vector constraints the range of pinning positions. Thelength of the virtual tape vector also allows for varying the smoothnessof the generated curve. This is because the input gesture space is“damped” as the vector gets longer. The length of this vector can becontrolled in several ways. In a two-handed operation mode, thenon-dominant hand (LH) controls the “pin” pivot point and the dominanthand (RH) controls the “tape” pivot point. Holding the “tape” pivotpoint stationary and moving the “pin” pivot point towards the “tape”pivot point shortens the vector, while moving the “pin” pivot point awayfrom the “tape” pivot point lengthens the vector. Similarly, holding the“pin” pivot point stationary and moving the “tape” pivot point shortensor lengthens the vector depending on direction of movement. In aone-handed operation, handles on a graphical widget (manipulator)holding both sensors are dragged to change vector length (or any othervaluator input device can be used, e.g., dial box).

The advantages over the traditional tape drawing technique are that thevirtual tape curves can be stored/retrieved electronically in variousformats (NURBS, polylines, etc), and easily transferred to CAD packages.Background images (engineering criteria) can be easilyoverlaid/underlaid to serve as reference material for the designer. Morecomplex editing operations (changing tape width, color) can be included.As well, predefined components or templates of commonly used parts orshapes (e.g., wheel well of cars, bumpers) can be imported from alibrary. This alleviates having to recreate standard items repeatedly.

The hardware components of the system 10 of the present invention, asdepicted in FIG. 1, preferably include a work station type computer 12,such as a Pentium II™ class machine running Microsoft Windows™, capableof using a rear screen projector 14 to project an image being drawn ontoscreen 16 which is viewed from a side opposite the projector 14. Mostautomotive design studios have a variety of large scale verticalcomputer display systems, often called “power-walls.” These power-walldisplays use state-of-the-art rear or front projection technology. Veryhigh resolution is achieved by using multiple projectors side-by-sidewith a slight overlap in images to create a single seamless large image.Image size can range from 8×6 to 50×10 feet. These displays aretypically used to display full-size images of car designs during thedesign and engineering process. These existing displays can be used asan output medium as well as a surface for digital tape drawings. Atypical system could use a Hughes/JVC G1000 digital projector with atrue 1280×1024 image back-projected onto a collapsible 8×6 ft. screen.The 8×6 ft. screen generally represents a minimum power-wall size, is ona scale equivalent to the size of a man, and is sufficient to implementthe tape drawing interaction techniques described herein that utilizelarge scale gestures. Large format plasma display screens used in HDTVapplications can also be used as the display 16. The invention can alsobe implemented using much smaller screens such as those found on desktopcomputers or laptops can also be used. The computer also includesstorage, such as disk storage, suitable for storing and distributing theprocesses of the present invention.

Since tape drawing naturally uses both hands, the invention needs to beable to sense the position of both hands on the display surface. Thereare several solutions to this sensing problem. These include opticaltracking techniques, the use of a transparent digitizing tablet on thedisplay surface, touch sensitive transparent display surfaces, andelectromagnetic/ultrasonic trackers. The present invention preferablyuses an electromagnetic tracker system having a left hand (LH) positiontracker 18 and right hand (RH) position tracker 20 whose positions aresensed by a position sensing module 22. The trackers preferably are heldat the surface of the display 16 or actually moved (slid) against thesurface of the display 16 and cursors corresponding to the trackers arecreated on the display 16 at the position of the trackers on thedisplay. The trackers can also be held at some distance from the display16 but this is not preferred because the correspondence between theposition of the tracker and the associated cursor becomes less apparentto the user. A suitable position tracking system is the AscensionFlock-of-Birds six degree-of-freedom electromagnetic tracker systemavailable from Ascension Technologies Inc. Each tracker 18 and 20 isaugmented with a switch used to control the effect of the tracker duringthe drawing process, as will be discussed in more detail later herein.

A first need of a digital tape drawing system is the ability to lay downdigital tape segments on the display/drawing surface. The inventionreplicates, as closely as possible, the capabilities and characteristicsof the physical tape laying process. In the physical media, the righthand (or dominant hand) unrolls the tape, while the left hand (ornon-dominant hand) slides along the tape while fastening it to thesurface. To create a continuous smooth line, tension in the tape must bemaintained between the two hands. If the right hand is held steady whilethe left hand fastens, the result is a straight line. The segment ofunfastened tape between the two hands can serve as a preview of theline. Curves are obtained by simultaneously moving the right hand in anappropriate arc while fastening with the left hand.

These techniques are preserved in the digital tape laying system, of thepresent invention. The present invention operates in a number ofdifferent states, as depicted in the state diagram of FIG. 2, that aredetermined by the positions of buttons on the position trackers 18 and20 where LB↑ indicates that the left hand button is up or not activated(b=0), LB↓ indicates that the left hand button is down or activated(b=1) with similar symbols for the right hand.

The first state 32 is the stretch tape state and involves the“stretching” of tape from the cursor 0 on the display 16 representingthe position of the LH tracker 18 to the cursor X representing the RHtracker 20 on the display 16. If “black” tape is being used thisstretched tape or unfastened tape segment shows up on the display asgrey or what could be called the shadow of the tape since it isemulating the tape being held in the air apart from the board before itis attached to or stuck to the board. The operations in state 32 will bediscussed in more detail later with respect to FIGS. 3A-3B and 4.

The second state 34 is the stick tape state where the stretched tape isstuck to the display by the left hand (tracker 18) moving along theunfastened tape toward the right hand (tracker 20). At the points wherethe tape is attached or “fastened” to the board the unfastened tape isconverted into “black” tape. The operations in this state will bediscussed in more detail with respect to FIGS. 5A, 5B and 6.

The third state 36 or terminate tape strip state is where the user hasdecided that this segment of tape is to end on the display 16. This issimilar the user tearing off the end of the tape at the end of a tapedline. The operations in this state will be discussed in more detail withrespect to FIGS. 5D and 8.

The stick/unstick state 38 is a state where tape that has been attachedto the display can be “pulled” off and reattached. The operations inthis state will be discussed in more detail with respect to FIGS. 5C, 6and 7.

The cut tape state 40 is a state where a section of tape that has beenattached to the display is removed and will be discussed in more detailwith respect to FIGS. 10A-10D and 11.

In the laying of tape on the display, by default, the right handcontrols a cursor which represents the roll of tape where this“roll-of-tape” cursor is represented by an “X” (see FIGS. 3A and 3B).The left hand controls a second cursor representing the end of theunfastened tape where this “end-of-tape” cursor is represented by “O”.Both cursors are controlled in a 1-1 manner by the trackers 18 (“O”) and20 (“X”) which operate in an absolute, linear position control mode. Asegment 44 of digital tape, represented as a polyline, always extendsbetween the two cursors from the left hand cursor O to the right handcursor X. This is referred to as the unfastened tape segment. Thedigital tape is preferably represented as a 1 cm thick line on thepreferred display 16. Moving the two hands around effectively moves theunfastened tape segment on the screen. The distance between the twohands determines the length of this unfastened tape segment. FIGS. 3Aand 3B illustrate unfastened tape segments 44 (dashed lines) extendedbetween the two cursors when the tracker buttons are not pressed (b=0).The length, position, and orientation of this unfastened tape segmentcan be changed by moving the cursors as shown by comparing FIGS. 3A and3B.

The operations in the stretch tape state 32 are depicted in FIG. 4. Notethat the actions performed are shown in the form of flowchartsoperations for convenience of description whereas it is preferable thatthe operations be performed in an interrupt based environment where theoperations are not necessarily performed in the order shown.Additionally, operating in the background, but not shown, are routinesthat monitor for changes in position of the buttons on the tracker aswell as monitor for changes in position of the trackers 18 and 20themselves. When one or both of the trackers have moved, the systemdetermines 62 (see FIG. 4) the new positions of the correspondingcursors and displays them at the new positions on the display 16. Thesystem then calculates 64 a vector from the left hand cursor (O) to theright hand cursor (X) in display space and creates a display linebetween the cursors along the vector between the cursors. As a result,each time a tracker is moved the unfastened tape segment moves while inthis state 34.

To “fasten” portions of the digital tape, the left hand presses thebutton on its tracker (left hand button b=1) putting the system into the“fasten mode.” This corresponds to the act of pressing down on the tapein the physical version. Releasing the left hand button (b=0) cuts thetape currently being laid at the position of the left hand cursor, aswill be discussed below.

In a manner similar to drawing with physical tape, straight lines arecreated by holding the right hand steady while the left hand, withtracker button pressed, slides along the unfastened tape segment towardsthe right hand, fastening the tape as it moves. While in the physicalversion the tape itself serves as a constraint for creating straightlines, the digital version of the present invention enforces thisconstraint in software by restricting the left hand cursor to move onlyalong the unfastened digital tape segment 44, towards the right handcursor (X). This ensures that once digitally fastened, the digital tapecannot be unfastened inadvertently (without invoking an edit operationto be described later). If the absolute left hand tracker positionstrays from the unfastened digital tape segment, the left hand cursorposition is determined by a simple projection of LH tracker position tothe nearest point on the unfastened tape segment. This is illustrated inFIGS. 5A-5D.

To start taping a straight line, the left hand tracker button is pressed(LH, b=1), as shown in FIG. 5A. Keeping the right hand in a fixedposition, the left hand lays down tape 74 as it slides along theunfastened tape segment 44 between the two cursors, as shown in FIG. 5B.Movement of the left hand cursor is constrained to the (closest point onthe) unfastened tape segment in the direction towards the right handcursor. A tape segment can be unfastened (undo) by pressing the righthand tracker button (RH, b=1) and backtracking along the previously laidtape with the left hand as shown in FIG. 5C. That is, the left hand ismoved backward along the path of the fastened tape. Again, the movementof the left hand cursor is constrained to the closest point along thefastened tape segment. Releasing the left hand tracker button (LH, b=0)cuts the tape at the location of the left hand cursor, as shown in FIG.5D, and returns the system to the default state shown in FIGS. 3A and3B.

When fastening tape in state 34, the system, upon the detection of themovement of the left hand tracker 18, determines 82, as shown in FIG. 6,whether the left hand tracker 18 (or cursor O) is moving toward theright hand tracker 20 (or cursor X). If not, such as the left hand ismoving away, no action occurs. If the left hand tracker 18 is movingtoward the right hand tracker 20, the system determines 84 the closestpoint on the unfastened tape 44 to the current position of the left handtracker. This point on the unfastened tape is compared to the mostrecent point of fastened tape 74 (solid line) or the cursor O and thesegment of unfastened tape in between the closest and most recent pointsis converted 86 from unfastened tape 44 to fastened tape 74 and thecursor is moved to this closest point.

When unsticking tape in state 38 (see FIG. 7), the system, upon thedetection of the movement of the left hand tracker 18, determines 92whether the left hand tracker 18 (or cursor O) is moving away from theright hand tracker 20 (or cursor X). If not, such as the left hand ismoving toward the right hand then the stick state of FIG. 6 occurs 94.If the left hand tracker 18 is moving away from the right hand tracker20, the system determines 96 the closest point on the fastened tape 74to the current position of the left hand tracker. This point on thefastened tape 74 is compared to the most recent point of unfastened tape44 or the cursor O and the segment of fastened tape in between theclosest and most recent points are converted 98 from fastened tape 74 tounfastened tape 44 and the cursor O is moved to the end of the fastenedtape line.

As shown in FIG. 8, when in the terminate tape state 36, the systemdetermines 102 the closest position of the left hand tracker 18 to thefastened tape 74 and detaches 104 the cursor from the end of thefastened tape line and positions the left hand cursor O under the lefthand tracker 18 or at a corresponding offset position as desired.

Creating curves with the invention mimics the physical equivalent.Unlike the creation of straight lines, both hands must move at the sametime. Thus, the unfastened tape segment moves while the left handfastens the tape. The length of the unfastened tape segment (or thelength of the vector between the left and right hands cursors/trackers)effectively serves to regulate the smoothness of the resulting curve.Since the left hand cursor is constrained to move along the unfastenedtape segment, a longer segment effectively reduces the range of movementof the fastening point controlled by the left hand, resulting insmoother curves (i.e., curve whose tangent changes gradually). A short(approaching zero) unfastened tape segment length reduces the techniqueto the equivalent of free-hand sketching with the non-dominant hand. Azero or approaching zero vector length occurs when the trackers are atthe same relative position on the display—possibly physically on top ofeach other. An interesting aspect of this technique is that iteffectively uses constrained two-handed gestures to control thesmoothness of curves. In contrast, most computer tools for generatingcurves rely on mathematical approaches for specifying smoothness. Forexample, holding both trackers in a single hand so that there is a fixeddistance between the trackers damps out random hand movements duringfreehand drawing.

To start taping a curve, the left hand tracker button is pressed (LH,b=1), as depicted in FIG. 9A. While moving the right hand (the Xcursor), the left hand (cursor O) lays down tape as it slides along theunfastened tape segment between the two cursors as shown in FIG. 9B.That is, in making a curve both the left and the right hands are movingsimultaneously which is in contrast to laying a straight line where theleft hand moves while the right hand stays fixed. Movement of the lefthand cursor is constrained to the (closest position on the) unfastenedtape segment in the direction towards the right hand cursor. A longunfastened tape segment results in smooth curves with a graduallychanging tangent, such as shown in FIG. 9B. Reducing the length of theunfastened tape segment, as shown in FIG. 9C, permits the generation ofhigher variation curves with a more rapidly changing tangent. The lengthof the unfastened tape segment can be changed on-the-fly simply bymoving the two cursors (and corresponding trackers) closer or fartherapart. Switching from taping curves to taping straight lines is achievedby simply keeping the right hand cursor in a fixed position while tapingwith the left hand, as shown in FIG. 9D. An explicit mode switch is notrequired. Releasing the left hand tracker button cuts the tape, asdepicted in FIG. 9E.

From the perspective of two-handed interaction, the tape layingtechniques of the present invention are powerful in that they allow forthe generation of straight lines and curves without a conventional modeswitch action such as the pressing of a switch or the selection of amenu item. The simple act of moving or not moving the right hand whilethe digital tape is being fastened determines whether a straight line orcurve is generated. That is, a mode switch between curves and straightlines (and visa versa) occurs via a motion associated with drawingrather than a motion associated with selection.

As with laying down tape, the invention's editing operations alsoemulate the physical process. First is the ability to undo the tapecurrently being laid down. In the physical media, the artist simply hasto pull the tape off the surface. In practice, the lack of physicaladhesion of the digital tape (we have virtual adhesion) results in usersnot always operating directly on the display surface, but often holdtheir hands and “float” a few inches above the surface. Thus, the undooperation preferably requires that the user explicitly press the buttonon the right hand tracker (RH, b=1). This allows the left hand to pullback on or detach the fastened tape. Since the left hand must be in“fasten mode” (i.e., its tracker button is pressed—LH, b=1), it canquickly relay the tape if desired.

The second editing operation is cutting of tape segments and is the cuttape state 40 of FIG. 2. Similar to cutting physical tape, the digitalversion requires that the user specify two cut points on the tape. Thisis done by pressing the right hand tracker button, with the left handtracker button not pressed (i.e., it is not in “fasten mode”), andspecifying the two cut points in turn. When the second cut point isspecified, the tape segment of a curve between the two points isremoved. At any time, a partially executed cut operation can be abortedby pressing the left hand tracker button and returning to “fasten mode.”

As shown in FIG. 10A, when not in tape laying mode (i.e., the left handtracker button is not pressed—LH, b=0), pressing the right hand trackerbutton (RH, b=1) engages the cut mode. The left hand cursor (O) ishidden. With the right hand button pressed, the right hand makes thefirst cut point 124 by moving the right hand cursor (X) across the tapeas shown in FIG. 10B. When the second cut point 126 is specified byagain passing the cursor (X) over the tape, the tape segment between thetwo cut points is removed as shown in FIG. 10C. The process can berepeated to cut additional tape segments if desired. Releasing the righthand tracker button completes the cut operation and returns the systemto the default stick tape mode with both cursors displayed as shown inFIG. 10D.

In performing the cutting operation, the system monitors for and detects132 the first cut point by detecting the intersection of the right handcursor X with the fastened tape 74 as shown in FIG. 11. The second cutpoint detected 134 is the next intersection point of the cursor X andthe tape 74. When the second cut point is determined the system removes136 the tape between the two cut points on the curve.

In traditional tape drawing, tapes of various widths are used to createvarious effects. For example, a thick physical tape is harder to bendduring the laying of a curved tape section than thin tape allowingsmoother large radius curves to be created with thicker tape. The widthof the tape determines the degree to which the tape that is being stuckon a board can be bent in a direction perpendicular to its width withouttearing. This stiffness limitation is simulated in the present inventionby limiting the maximum amount of rotation of the vector going from thepinning hand to the non-pinning hand from its original position to anamount corresponding to 1/w where w is the width. Tape width changes canbe accomplished by changing the tape parameter or using a different setof input devices.

The tensile strength of physical tape also limits the ability of thetape to bend. This can also be simulated in the present invention byproviding a tensile strength parameter that inversely controls theallowed amount of bending of the tape to the width discussed above. Thatis, with the bending or maximum rotation of the vector limited by 1/twhere t is the tensile strength, the system provides tape limited bytensile strength.

In addition to the core operations of laying and editing tape, thepresent invention also support several additional operations.Traditional tape artists typically draw on a surface with an underlaidgrid. The invention provides a similar functionality by conventionallydisplaying a reference grid on the large scale display 16 that can betoggled on/off via a keyboard. Also, tape drawings are often made withreference to engineering specifications (called the “engineeringpackage”) that delimit the unchangeable dimensions of a car'scomponents. The designer has to work within this engineering framework.In the physical media, this package information is simply printed ontolarge size paper and attached to the tape drawing surface. The inventionprovides this functionality in two ways. First, the system has theability to conventionally import this information which is thendisplayed as a background image in the large screen projection. Second,in the invention, the background of the tape drawing application windowis conventionally made transparent and thus tape drawings can be createdon top of any other application window. This allows for drawings to becreated right over the application used to create the engineeringpackage and, thus, on the top of previously existing drawings. Theinvention also provides the ability to save and load tape drawingsto/from files using conventional file saving techniques. The file formatcan be read by other 3D automotive modeling applications, such as AliasAutostudio™.

The present invention provides for seamless mode switching that could beapplied to other two-handed systems. Based on whether the two cursorsare moving simultaneously or in sequential manner, the invention(implicitly) switches between two modes (in the present case, drawingstraight lines or curves). In addition to using the temporalcharacteristics of the motions of the hands, the relative proximity ofthe hands is also used to invoke or switch to different functionality.For example, when drawing curves in the present invention, keeping thehands (trackers) close together results in high variation curves,whereas moving them apart resulted in smooth, gently varying curves.Another possible use of this proximity information is to display(perhaps by gradually fading in) a palette or menu when the hands areclose together.

Alternative input technologies can be used rather than theelectromagnetic senor system previously discussed. Wireless mice can beused. Hand held styli or light pens could also be used. If the displayscreen includes a touch sensitive input screen, such as can be attachedto a plasma display panel, the fingers of the user could act as theinput devices. The input devices could be provided with more than onebutton each which would allow the user to cause other actions to occursuch as the popping up of a transparent menu or window adjacent to oneof the users hands allowing the other hand to be used to select itemsfrom the menu.

The system can also be implemented on a desktop computer system using aCRT display screen and two input devices such as two pens on adigitizing tablet.

The cursors can be displayed directly beneath the absolute trackerposition as discussed previously herein. However, depending on theposition of the user this may result in the user's hand obscuring thecursor. To solve this problem the cursor is offset by a fixed distancefrom the hand/tracker.

Some users may object to the loss of physical tension between the twohands that is afforded by physical tape. Tensioning devices such asretractable tapes and elastic bands can be used to simulate thistension. In this embodiment an elastic band is attached between thetrackers 18 and 22.

Users may sometimes find it difficult to join tape segment endsaccurately. This can be solved by features like smart snapping ofendpoints when desired which involves causing a tape end to move to theclosest endpoint when a join operation is in progress.

A curve inspection technique, called “sighting down the curve” iscommonly used in the physical media to check the smoothness of thecurve. While it is possible to “sight down a curve” on the large scaledisplay in the digital tape drawing system of the invention, aprojection screen having a slight convex curvature facilitates thisinspection operation.

Using a pop-up menu or transparent underlay menu or tool palette, theuser can be given access to sophisticated editing and paintingfacilities which would allow for advanced rendering effects such asairbrushing along the edges of curves, to create stylized renderings andcutting tools.

More sophisticated interaction techniques that go beyond mimickingtraditional tape operations and properties can also be provided. Forexample, some curve editing tools found in desktop applications, such astangency manipulators, would work on a power wall such as created withthe present invention.

To compare two tape drawings, a common drawing scale can be used. Thisallows two or more tape drawings to be superimposed and compared as wellas facilitates reusing portions of the drawings.

The tape drawing system of the invention can be integrated with existingcurve and surface evaluation computer packages.

The invention can be extended to offer traditional drawing tools such ascircles and rectangles which would be a time saving. Importing anddisplaying clip art and images (e.g., wheels, hub caps, interior consolecomponents like vents, stereo controls, basic materials like leather,vinyl, etc.) to augment the tape drawing is within the capabilities ofthe system.

A “ruler” mode can be provided that would measure the distance betweenthe two trackers in the current tape drawing scale. This would allow thecreation of accurately scaled drawings.

A flood “fill region” feature which fills in the space between tapelines with a specified fill, such as a color, reduces the time requiredfor the often quite laborious creation of a fill using strips ofphysical tape.

A symmetry drawing mode can be added which would lay down duplicatemirror-based curves given a predetermined input plane. This is motivatedby the fact that many components in a car have symmetrical counterparts(e.g., two headlights).

The present invention changes from not pinning to pinning by activatingthe button on the left hand input device. The change in state can alsoinitiated in other ways such as with pressure. For example, touchsensitive screens can sense pressure where a high pressure couldindicate a state change.

The present invention has been described with respect to using “digital”tape and a display upon which the tape is displayed. It is also possiblefor the trackers to be incorporated into a physical tape dispensingdevices for unrolling physical tape and into a roller for pressing thetape onto a tape drawing board. The physical tape could be applied to atape drawing board as in conventional tape drawing while the trackerscould be used to capture the laying of the electronic equivalent of thetape as previously discussed.

The present invention has been described with respect to a single userlaying tape at one time. It is possible for multiple pairs of inputdevices to be used at one time allowing a number of different designersto input at the same time. The tape laid by each of the individuals canbe distinguished by color.

The many features and advantages of the invention are apparent from thedetailed specification and, thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and changes will readily occur to those skilledin the art, it is not desired to limit the invention to the exactconstruction and operation illustrated and described, and accordinglyall suitable modifications and equivalents may be resorted to, fallingwithin the scope of the invention.

What is claimed is:
 1. A drawing system, comprising: a display; firstand second input devices held by corresponding hands of a user; and acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display during a two-handed drag operation by the user, wherethe corresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline.
 2. Adrawing system, comprising: a display; first and second input devicesheld by corresponding hands of a user; and a computer determiningcorresponding positions of said input devices on said display, anddrawing a polyline between the corresponding positions on said display,where the corresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline wherethe polyline is an unfastened drawing tape segment.
 3. A system asrecited in claim 1, wherein said display comprises a vertical displayhaving a scale equivalent to a size of a man.
 4. A system as recited inclaim 1, wherein said computer produces cursors on said display at thecorresponding positions.
 5. A system as recited in claim 1, wherein whensaid input devices move the polyline moves.
 6. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, where thecorresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline wherethe polyline drawn switches between a straight line and a curved lineresponsive to whether one of said input devices is moved individually orboth of said input devices are moved simultaneously.
 7. A drawingsystem, comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, where thecorresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline wheresaid system switches between modes based upon an automaticdetermination.
 8. A system as recited in claim 1, wherein a curvature ofa curved line drawn by said system corresponds to a distance betweensaid input devices.
 9. A drawing system, comprising: a display; firstand second input devices held by corresponding hands of a user; and acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline where a curvature of a curved line drawn by said systemcorresponds to a distance between said input devices and where curveline smoothness corresponds to the distance between said input devices.10. A drawing system, comprising: a display; first and second inputdevices held by corresponding hands of a user; and a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a polyline between the corresponding positions onsaid display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline where a fixed distance between said first and secondpositions when said input devices are held in a single hand damps outrandom hand movements made during freehand drawing.
 11. A drawingsystem, comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, where thecorresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline wherewhen said first and second input devices are at substantially a sameposition relative to said display, the user can freehand draw curves.12. A drawing system, comprising: a display; first and second inputdevices held by corresponding hands of a user; and a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a polyline between the corresponding positions onsaid display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline where a distance between said input devices is fixed andthe distance controls curve smoothness.
 13. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, where thecorresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline wheresaid polyline corresponds to unfastened drawing tape and when a firsthand moves toward a second hand while the system is in a tape stickstate, the unfastened tape is converted to fastened tape correspondingto a position of the first hand.
 14. A system as recited in claim 13,wherein a point of conversion of unfastened tape to fastened tape isconstrained to the polyline.
 15. A drawing system, comprising: adisplay; first and second input devices held by corresponding hands of auser; and a computer determining corresponding positions of said inputdevices on said display, and drawing a polyline between thecorresponding positions on said display, where the correspondingpositions of said input devices and at least one additional previousposition contribute to a shape of the polyline where the polylinecorresponds to fastened drawing tape and when a first hand moves awayfrom a second hand while the system is in a tape unstick state, thefastened tape is converted to unfastened tape corresponding to aposition of the first hand.
 16. A system as recited in claim 15, whereina point of conversion of fastened tape to unfastened tape is constrainedto the polyline.
 17. A drawing system, comprising: a display; first andsecond input devices held by corresponding hands of a user; and acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline where the polyline corresponds to fastened drawing tape andwhen a first hand crosses the fastened drawing tape at two cut points,the drawing tape between the two cut points along the polyline isremoved.
 18. A drawing system, comprising: a display; first and secondinput devices held by corresponding hands of a user; and a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a,polyline between the corresponding positions onsaid display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline where during curve drawing rotation of a vector between thetwo positions about a pin point is limited.
 19. A system as recited inclaim 18, wherein the rotation limitation corresponds to one of tapewidth and tensile strength.
 20. A drawing system, comprising: a display;first and second input devices held by corresponding hands of a user; acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline; and a tensioning device connected between said first andsecond input devices.
 21. A drawing system, comprising: a display; firstand second input devices held by corresponding hands of a user; acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display, where the corresponding positions of said input devicesand at least one additional previous position contribute to a shape ofthe polyline; and a tape dispensing device holding said first inputdevice and a tape roller holding said second input device.
 22. A drawingsystem, comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, where thecorresponding positions of said input devices and at least oneadditional previous position contribute to a shape of the polyline wheresaid display displays a graphic and the polyline is drawn over thegraphic.
 23. A system as recited in claim 1, wherein the polyline is acurve.
 24. A system as recited in claim 1, wherein the polyline iscapable of being pinned in place.
 25. A drawing system, comprising: adisplay; first and second input devices held by corresponding hands of auser; and a computer determining corresponding positions of said inputdevices on said display, and drawing a curve between the correspondingpositions on said display during a two-handed drag operation by theuser, where the corresponding positions of said input devices and atleast one additional previous position contribute to a shape of thecurve.
 26. A drawing system, comprising: a display; first and secondinput devices held by corresponding hands of a user; and a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a line between the corresponding positions on saiddisplay during a two-handed drag operation by the user with the linebeing capable of being pinned in place on said display.
 27. A drawingsystem, comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a linebetween the corresponding positions on said display with switchingbetween curve and straight line drawing modes being implicit.
 28. Anelectronic tape drawing system, comprising: a vertical display having ascale equivalent to a size of a man; first and second input devices heldby corresponding hands of a user; and a computer determiningcorresponding positions of said input devices on said display, producingcursors on said display at the corresponding positions, and drawing aline between the cursors on said display with the line drawing switchingbetween drawing a straight line and a curved line responsive to whetherone or both of said input devices are moved simultaneously and with acurvature of the curved line drawn by said system corresponding to adistance between said input devices, and when the line corresponds tounfastened drawing tape and a first hand moves toward a second handwhile the system is in a tape stick state, the unfastened tape isconverted to fastened tape corresponding to a position of the firsthand, when the line corresponds to fastened drawing tape and a firsthand moves away from a second hand while the system is in a tape unstickstate, the fastened tape is converted to unfastened tape correspondingto a position of the first hand with the point of conversion beingconstrained to the line, and when the line corresponds to fasteneddrawing tape and a first hand crosses the fastened drawing tape at twocut points, the drawing tape between the two cut points is removed. 29.A drawing system, comprising: display means for displaying graphics;first and second input means devices held by corresponding hands of auser and for designating positions of a line; and means for determiningcorresponding positions of the input means on the display, drawing aline between the corresponding positions on said display and switchingbetween drawing a straight line and a curved line responsive to whethersaid input means move simultaneously.
 30. A drawing method, comprising:inputting first and second input positions using corresponding hands ofa user during a two-handed drag operation by the user; and determiningcorresponding positions on a display; and drawing a polyline between thecorresponding positions on the display during the two-handed dragoperation.
 31. A drawing method, comprising: inputting first and secondinput positions using corresponding hands of a user; and determiningcorresponding positions on a display; and drawing a polyline between thecorresponding positions on the display where said drawing switchesbetween straight and curved line drawing responsive to whether the firstand second input positions move simultaneously.
 32. A drawing method,comprising: inputting first and second input positions usingcorresponding hands of a user; and determining corresponding positionson a display; and drawing a polyline between the corresponding positionson the display where when a first input position moves toward a secondinput position while in a tape stick state, unfastened tape is convertedto fastened tape corresponding to a the first input position.
 33. Adrawing method, comprising: inputting first and second input positionsusing corresponding hands of a user; and determining correspondingpositions on a display; and drawing a polyline between the correspondingpositions on the display where when a first input position moves awayfrom a second input position hand while in a tape unstick state,fastened tape is converted to unfastened tape corresponding to the firstinput position.
 34. A drawing method, comprising: inputting first andsecond input positions using corresponding hands of a user; anddetermining corresponding positions on a display; and drawing a polylinebetween the corresponding positions on the display where when a firstinput position crosses fastened drawing tape at two cut points, thedrawing tape between the two cut points is removed.
 35. A computerreadable storage for controlling a computer by determining correspondingpositions on a display for first and second input positionscorresponding hands of a user as the user performs a two-handed dragoperation and drawing a polyline between the corresponding positions onsaid display during the two-handed drag operation, where thecorresponding positions and at least one additional previous positioncontribute to a shape of the polyline.
 36. A drawing system, comprising:a display; first and second input devices held by corresponding hands ofa user; and a computer determining corresponding positions of said inputdevices on said display, and drawing a polyline between thecorresponding positions on said display, wherein the polyline is anunfastened drawing tape segment.
 37. A drawing system, comprising: adisplay; first and second input devices held by corresponding hands of auser; and a computer determining corresponding positions of said inputdevices on said display, and drawing a polyline between thecorresponding positions on said display during a two-handed dragoperation by the user, wherein said display comprises a vertical displayhaving a scale equivalent to a size of a man.
 38. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, wherein thepolyline drawn switches between a straight line and a curved lineresponsive to whether one or both of said input devices are movedsimultaneously.
 39. A drawing system, comprising: a display; first andsecond input devices held by corresponding hands of a user; and acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display, wherein said system switches between modes based uponan automatic determination.
 40. A drawing system, comprising: a display;first and second input devices held by corresponding hands of a user;and a computer determining corresponding positions of said input deviceson said display, and drawing a polyline between the correspondingpositions on said display during a two-handed drag operation by theuser, wherein a curvature of a curved line drawn by said systemcorresponds to a distance between said input devices.
 41. A drawingsystem, comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, wherein curve linesmoothness corresponds to the distance between said input devices.
 42. Adrawing system, comprising: a display; first and second input devicesheld by corresponding hands of a user; and a computer determiningcorresponding positions of said input devices on said display, anddrawing a polyline between the corresponding positions on said display,wherein a fixed distance between said first and second positions whensaid input devices are held in a single hand damps out random handmovements made during freehand drawing.
 43. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, wherein when saidfirst and second input devices are at substantially a same positionrelative to said display, the user can freehand draw curves.
 44. Adrawing system, comprising: a display; first and second input devicesheld by corresponding hands of a user; and a computer determiningcorresponding positions of said input devices on said display, anddrawing a polyline between the corresponding positions on said display,wherein a distance between said input devices is fixed and the distancecontrols curve smoothness.
 45. A drawing system, comprising: a display;first and second input devices held by corresponding hands of a user;and a computer determining corresponding positions of said input deviceson said display, and drawing a polyline between the correspondingpositions on said display, wherein said polyline corresponds tounfastened drawing tape and when a first hand moves toward a second handwhile the system is in a tape stick state, the unfastened tape isconverted to fastened tape corresponding to a position of the firsthand.
 46. A drawing system, comprising: a display; first and secondinput devices held by corresponding hands of a user; and a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a polyline between the corresponding positions onsaid display, wherein a point of conversion of unfastened tape tofastened tape is constrained to the polyline.
 47. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, wherein thepolyline corresponds to fastened drawing tape and when a first handmoves away from a second hand while the system is in a tape unstickstate, the fastened tape is converted to unfastened tape correspondingto a position of the first hand.
 48. A drawing system, comprising: adisplay; first and second input devices held by corresponding hands of auser; and a computer determining corresponding positions of said inputdevices on said display, and drawing a polyline between thecorresponding positions on said display, wherein a point of conversionof fastened tape to unfastened tape is constrained to the polyline. 49.A drawing system, comprising: a display; first and second input devicesheld by corresponding hands of a user; and a computer determiningcorresponding positions of said input devices on said display, anddrawing a polyline between the corresponding positions on said display,wherein the polyline corresponds to fastened drawing tape and when afirst hand crosses the fastened drawing tape at two cut points, thedrawing tape between the two cut points along the polyline is removed.50. A drawing system, comprising: a display; first and second inputdevices held by corresponding hands of a user; and a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a polyline between the corresponding positions onsaid display, wherein during curve drawing rotation of a vector betweenthe two positions about a pin point is limited.
 51. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display, wherein therotation limitation corresponds to one of tape width and tensilestrength.
 52. A drawing system, comprising: a display; first and secondinput devices held by corresponding hands of a user; a computerdetermining corresponding positions of said input devices on saiddisplay, and drawing a polyline between the corresponding positions onsaid display; and a tensioning device connected between said first andsecond input devices.
 53. A drawing system, comprising: a display; firstand second input devices held by corresponding hands of a user; acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display; and a tape dispensing device holding said first inputdevice and a tape roller holding said second input device.
 54. A drawingmethod, comprising: inputting first and second input positions usingcorresponding hands of a user; and determining corresponding positionson a display; and drawing a polyline between the corresponding positionson the display, wherein said drawing switches between straight andcurved line drawing responsive to whether the first and second inputpositions move simultaneously.
 55. A drawing method, comprising:inputting first and second input positions using corresponding hands ofa user; and determining corresponding positions on a display; anddrawing a polyline between the corresponding positions on the display,wherein when a first input position moves toward a second input positionwhile in a tape stick state, unfastened tape is converted to fastenedtape corresponding to a the first input position.
 56. A drawing method,comprising: inputting first and second input positions usingcorresponding hands of a user; and determining corresponding positionson a display; and drawing a polyline between the corresponding positionson the display, wherein when a first input position moves away from asecond input position hand while in a tape unstick state, fastened tapeis converted to unfastened tape corresponding to the first inputposition.
 57. A drawing method, comprising: inputting first and secondinput positions using corresponding hands of a user; determiningcorresponding positions on a display; and drawing a polyline between thecorresponding positions on the display, wherein when a first inputposition crosses fastened drawing tape at two cut points, the drawingtape between the two cut points is removed.
 58. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display during a two-handeddrag operation by the user, wherein said display displays a graphic andthe polyline is drawn over the graphic.
 59. A drawing system,comprising: a display; first and second input devices held bycorresponding hands of a user; and a computer determining correspondingpositions of said input devices on said display, and drawing a polylinebetween the corresponding positions on said display during a two-handeddrag operation by the user, wherein the polyline is capable of beingpinned in place.
 60. A drawing system, comprising: a display; first andsecond input devices held by corresponding hands of a user; and acomputer determining corresponding positions of said input devices onsaid display, and drawing a polyline between the corresponding positionson said display as the user performs a two handed drag operation bymoving both input devices.